The disclosure herein relates generally to implantable orthopedic prosthesis and, more particularly, to new methods for preparing and cutting the radial and carpal bones to receive a wrist prosthesis.
Contemporary methods to implant prosthetic wrists have a number of disadvantages. During a total wrist arthroplasty, for example, the intramedullary canal of the radius is reamed and broached, and the end of the radius is cut. The carpal bones are then cut xe2x80x9cfree-hand.xe2x80x9d In other words, instruments are often not used to align the cut angles or provide a guide for a planar cut. Further, these cuts are made without using instruments to reference back to cuts made on the radial bone. The cuts on the carpal bone, then, depend heavily on the skill, accuracy, and judgment of the particular surgeon.
One important criteria in wrist arthroplasty is xe2x80x9cmeasured resection.xe2x80x9d Here, the amount of bone resected should be commensurate with the size of the implant; excessive amounts of bone should not be removed. If too much bone and tissue are removed, the bone can become weak and susceptible to postoperative fracture. If such a fracture occurs, sufficient bone may not remain to permit a satisfactory fusion procedure. Further, the bone may be too weak or too small for subsequent revision or corrective surgical procedures.
As another important criteria in wrist arthroplasty, the cuts on the end of the radial and carpal bones should be made with consistency and precision. If great skill is not used to perform these cuts, the prosthetic wrist implant may not fit well in the bone. As a result, the patient may lose some functionality or experience an unwanted decrease in the range of motion.
The radial and carpal bone cuts are particularly important because prosthetic wrists are manufactured in a limited number of sizes, often +1, +2, and +3 mm. If the cuts are not made in the proper location or with proper alignment, then none of the three sizes of implants may correctly fit.
It therefore would be advantageous to provide new methods for preparing and cutting the radial and carpal bones to receive a wrist prosthesis. Such methods could maximize accuracy and precision of cuts on the carpal and radial bones and simultaneously minimize the amount of bone being resected.
The present invention is directed toward a method for preparing and cutting the radial and carpal bones to receive a prosthetic wrist during, for example, a total wrist arthroplasty.
One important advantage of the present invention is the amount of bone resected from the radial and carpal bones corresponds to the exact size of the implant to be implanted. Unnecessary bone is not removed. As such, the implant is less susceptible to postoperative fracture due to unwanted bone resection. Further, the prosthetic implant more closely matches the natural wrist and enables a fuller natural range of motion to the patient.
During the first steps of the present invention, the intramedullary canal of the radial bone is reamed. First, a k-wire is placed into the canal, and the position of this wire is visually verified on a fluoroscope. The k-wire, thus, previews the path of the reamer before the canal is reamed. During reaming, the k-wire provides a visual path for the reamer, so the reamer can more successfully be aimed down the canal. The step of using a k-wire helps to ensure that the intramedullary canal of the radial bone is reamed with consistency and precision.
After the canal is reamed, it is broached with a broach having two segments that are removeably connectable to each other. The broach is impacted into the canal, and the handle portion of the broach is removed. A broach segment of the broach, however, is left in the canal. This broach segment is used as both a guide and a reference to cut the end of the radial bone. The broach segment further replicates the actual size of the end of the radial implant to be implanted in the radial bone. Since radial cuts are made with reference to the position of the broach in the intramedullary canal, unnecessary bone is not removed. Further, reference from the broach ensures that the size and shape of the end portion of the radial implant will match the size and shape of the bore in the canal.
In order to perform the cuts on the radial bone, a cutting tool or planer is attached to the broach segment embedded in the canal. The cutting tool is then guided down with the broach segment to cut the end of the radial bone. The cutting tool cuts a plateau or flat surface that matches and aligns with the top, flat surface of the implant.
Next, the carpal bones are cut. In particular, a cut block is connected to the end of the broach segment while it is still embedded in the intramedullary canal of the radius. The cut block has a cutting slot that is aligned to cut the carpal bones in the exact location where the carpal baseplate will be located.
Cutting the carpal bones from the broach segment while it is embedded in the intramedullary canal of the radius has many advantages. For instance, the cut on the end of the carpal bone can be made with consistency and precision. A xe2x80x9cfree-handxe2x80x9d cut is not used. Further, the cuts on the carpal bone are made while being referenced to the previous cut on the radial bone. Additionally, the cut block has a thickness that exactly matches the size of implant to be implanted. As such, excess bone is not removed from the carpal bones.